GHWB *was* pro-abort when he ran for president in 1980, but converted to pro-life at some point during the Reagan admin. The change in positions was apparently sincere and lasting, and the Bushes had dinner table arguments on the subject with Barbara on one side and GHW, GW, Jeb on the other.
I'm not familiar with the reason for GHWB's change on the issue, but considering he'd already run strongly for president before it's hard to compare it to Mitt's "I'm pro-abortion in Massachusetts" oops now I'm gonna call myself pro-life without giving specifics so I can run for president.